Non-metal reinforced self-baking electrode for electric furnaces



Aug. 11, 1970 I J VAN NOSTRAN EI'AL 3,524,004

. NON-METAL REINFORCED SELF-BAKING ELECTRODE FOR ELECTRIC FURNACES Filed Dec. 5, 1968 2 Sheets-Sheet l INVENTORS' Judi/A. Vm/ Nbslrwzv ATTORNEYS and OZisDJorolwn I WW1Q Aug. 11, 1970 J N os- EAL 3,524,004

NON-METAL REINFORCED SELF-BAKING ELECTRODE FOR ELECTRIC FURNACES Filed Dec. :3, 1968 2 Sheets-Sheet 2 39 S ITW 1 1 {111 1111 F 2 INVENTORS.

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ATTORNEYS United States Patent 3,524,004 NON-METAL REINFORCED SELF-BAKING ELECTRODE FOR ELECTRIC FURNACES Jack A. Van Nostran and Otis D. Jordan, North Canton,

Ohio, assignors to Ohio Ferro-Alloys Corporation,

Canton, Ohio, a corporation of Ohio Filed Dec. 3, 1968, Ser. No. 780,668 Int. Cl. H05b 7/18, 3/62, 3/40 U.S. C]. 13-14 14 Claims ABSTRACT OF THE DISCLOSURE to a lain transformer or other conventional source of electric power. A ball and socket rotating contact and non-rotating contact assembly is provided at the upper end of the tube and is connected by conductors with the electric power source, or to power factor correctional devices if desired. Carbon paste is inserted into the open tops of the cylinder and tube and as the paste descends into the heat zone of the furnace it first becomes plastic and completely fills the cylinder and tube, and then undergose a coking or baking process and becomes hard carbon. From time to time, as the lower end 0 the hard carbon electrode is burned away in the furnace charge, the tube may be rotated within the hard carbon electrode causing it to slide downward through the easing into the furnace charge.

BACKGROUND OF THE INVENTION Field of the invention The invention relates to the construction and use of self-baking electrodes in electric arc furnaces and to a novel method of producing such electrodes, and more particularly to an improvement in the art of making and using self-baking electrodes in which virtually no metal is introduced into the furnace charge by the electrode.

Description of the prior art Under present practice, self-baking or Soderberg-type electrodes are produced in electric furnaces by suspending in the furnace cylindrical steel casings of the diameter of the desired electrode.

These casings are held in the support clamps and electrical power clamps ordinarily used to support electrodes in electric furnaces and to conduct electric power thereto, and they extend from the crucible of the furnace upward to an area above the furnace, passing through hoods or covers and having their upper open ends in an area wherein men may work.

Each casing is provided with a number of internal reinforcing fins equally spaced around the inside perimeter of the casing and extending radially toward the axis thereof. These fins not only reinforce the electrode in its formative stage but also serve to conduct electrical current from the electric contact clamps to the cured or hardened portions of the electrode, and further serve the purpose of conducting heat from the cured or hardened portions of the electrode to those portions thereof that are in the process of curing and for which purpose much heat is required.

These casings are filled from above with carbon paste, which is a mixture of powdered anthracite coal, powdered coke and pitch. As this carbon paste descends into the heat zone of the furnace, it first becomes plastic and completely fills the casing, after which it undergoes a coking or baking process and becomes hard carbon before it finally descends into the crucible zone of the furnace.

As an electrode is consumed, new sections of metal casing are welded to the top thereof, at both the junctures of the casing sections and the reinforcing fins therein, to make a continuous unit of uniform strength and conductivity.

As the lower portion of an electrode is consumed the clamps are operated in conventional manner to lower the self-baked electrode, including the steel casing in which it is enclosed, thus introducing the steel casing, with the steel reinforcing fins therein, into the furnace charge.

The iron contained in the casing and fins is consumed by the furnace and enters into the product being made in the furnace. Since iron cannot be tolerated in some products, it has not heretofore been possible to use selfbaking electrodes in furnaces making such products.

In an effort to overcome this problem, the outer casing has been constructed separately from a centrally located reinforcing lattice or Christmas tree of stainless steel imbedded in the electrode and supporting the weight of the same.

The electrode is formed of carbon paste which is hardened in the manner above described and the hard carbon portion thereof is progressed into the furnace at the required rate, while the outer casing is progressed through the holders at the minimum rate possible, resulting in a differential rate of progression between the electrode and the outer steel casing thereof.

Although this construction reduces to some degree the amount of iron carried into the furnace by the steel casing of the electrode, it has serious disadvantages as follows:

First, the metal contained in the central support lattice or Christmas tree is carried into the furnace charge. For this reason the lattice or Christmas tree must be of very light construction to limit this contamination of the product with iron.

Secondly, the necessarily light construction of the central support lattice or Christmas tree renders it ineffective for the purpose of inducting heat from the cured or hardened carbon portion of the electrode to the plastic portions thereof.

Thirdly, since the central support lattice or Christmas tree is not attached to the cylindrical steel casing, no electrical power is made to flow into the central portions of the electrode such as is the case when reinforcing fins are attached to the interior of the casing.

Thus, the heating and curing effect of the electrical current is lacking in the central portions of such electrodes, thus limiting the possible diameter of any electrode thus produced. In actual practice, such electrodes have, as of the present, been limited to approximately 40 inches in diameter.

SUMMARY OF THE INVENTION In general terms, the invention may be briefly described as including a cylindrical metal casing extending into the top of an electric furnace, casing support clamp means around an intermediate portion of the casing and suspending it from a support header by means of hydraulic cylinders, contact clamps around the lower end portion of the casing and connected by conductors to a source of electrical power such as a transformer. The contact clamps are carried by a support structure to which the support header is attached. This support structure extends upwardly and is supported by hydraulic cylinders which may be actuated to move the entire electrode column vertically in either direction relative to the furnace.

The support structure carries a nonrotating contact spaced above the top of the casing and concentric there with. Flexible conductors connect the nonrotating contact to the power source or to power factor correctional devices as desired. A rotating contact is journalled in the nonrotating contact or bearing in the form of a ball and socket joint.

This rotating contact is fixed to the upper end of a metal tube suspended axially within the casing and extending some distance below the same. The lower end of this metal tube has coarse deep screw threads formed upon its exterior. Any suitable method of rotation of the tube 28 may be provided.

The upper end for the electrode casing is open and extends upward through various hoods above the furnace in a conventional manner to an area suitable for workmen to occupy to add carbon paste to the casing as needed, and to weld casing sections upon the top of the casing if and when the same may be necessary.

The upper end of the metal tube is also open so that chunks of carbon paste may be added thereto as needed. The rotatable tube together with its rotating contact or journal and nonrotating contact or bearing are all constructed of a suitable strong and conductive metal.

As the carbon paste descends into the hot zone of the furnace it first becomes plastic and completely fills the casing, after which it undergoes a coking or baking process and becomes hard carbon. From time to time, as necessary, the support tube is rotated, unscrewing the hard carbon electrode therefrom and feeding it down out of the easing into the furnace charge.

As the chunks of carbon paste descend in the tube, the carbon paste becomes plastic and entirely fills the opening in the hard carbon electrode formed by the screw threads on the lower end of the tube, after which it is also cured or baked to become hard carbon.

It is, therefore, an object of the invention to provide a self-baking electrode for electric furnaces which eliminates virtually all metal from entering the furnace from either casing or central reinforcing structure.

Another object of the invention is to provide a selfbaking electrode of the character referred to which provides means whereby heat is effectively conducted from the hardened portions of the electrode to the plastic portions thereof.

A further object of the invention is to provide such a self-baking electrode which provides means whereby electrical currents are caused to flow through the central portions of the electrode in the curing zone.

A still further object of the invention is to provide a self-baking electrode of this type which is so constructed that it provides an improved distribution of electrical current in the electrode.

Another object of the invention is to provide a selfbaking electrode of the character referred to which greatly reduces, and in fact nearly eliminates, the casing used and thereby reduces electrode costs.

A further object of the invention is to provide such a self-baking electrode with improved means for progress ing an electrode or casing-enclosed electrode through the casing support clamps and contact clamps and into the furnace as required.

A still further object of the invention is to provide a self-baking electrode of this type having means for supporting and progressing the hardened electrode independently of the casing support clamps and contact clamps.

Another object of the invention is to provide a selfbaking electrode of the character referred to with means for conducting electrical current to the central portions of the electrode independently of the contact clamps.

A further object of the invention is to provide such a self-baking electrode with means for supporting and progressing the electrode on an axially disposed vertical feed screw.

A still further object of the invention is to provide a self-baking electrode of this type with means for causing electrical currents to flow to the central portions of the electrode by Way of said axially disposed feed screw.

Another object of the invention is to provide a selfbaking electrode of the character referred to with means for connecting power factor correctional and control devices to the electrode by way of said axially disposed feed screw.

It is also an object of the invention to provide such a self-baking electrode with a non-progressing axially disposed feed screw connecting the hardened portions of the electrode to a support and feed screw drive mechanism.

A further object of the invention is to provide a selfbaking electrode of this type in which the axially disposed feed screw is hollow.

A still further object of the invention is to provide a self-baking electrode of the character referred to having means for introducing carbon paste to the electrode baking zone by way of the hollow axially disposed feed screw.

It is another object of the invention to provide a selfbaking electrode of the character referred to in which the hollow feed screw is fluid cooled or heated.

And finally, it is an object of the invention to provide such a self-baking electrode with means for conducting electrical current between rotating and nonrotating parts of the feed screw mechanism.

These and other objects, apparent from the drawings and following description, may be attained, the abovedescribed difiiculties overcome and the advantages and results obtained, by the apparatus, construction, arrangement, and combinations, subcombinations and parts, and methods, steps, procedures, and modes of operation, which comprise the present invention, a preferred embodiment of which, illustrative of the best mode in which applicants have contemplated applying the principle, being set forth in detail in the following description and illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional view through self-baking electrode mechanism embodying the invention; and

FIG. 2 is a diagrammatic view showing the connection of the three electrodes of an electric furnace to a power factor correctional and control device including a deltadelta arrangement of transformers with means for connecting the same to capacitors.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now more particularly to the embodiment illustrated, the upper portion of a furnace charge is indicatcd at 1. The furnace itself is not illustrated in the drawings. As in usual practice, there are various hoods located above the furnace, one of which is indicated in FIG. 1 at 2.

Each self-baking electrode is formed within a vertically disposed, cylindrical, metal casing 3, the lower end of which extends into the furnace and terminates above the furnace charge while the upper end of the casing is open and extends upward through the various hoods such as 2, above the furnace, to an area suitable for workmen to occupy while adding carbon paste to the casing as needed, and while welding on a new casing section if and when the same should ever become necessary.

One purpose of the metal casing 3 is to contain and give proper form and support to the carbon paste 4 after it becomes plastic, as indicated at 4a, and until it has been cured and hardened into a hard carbon electrode, as seen at 411.

Another purpose of the metal casing 3 is to conduct electrical power from the contact clamps to the electrode 4b. Still another purpose of this metal casing is to conduct heat from the furnace charge 1 and the electrode 4b to the carbon paste 4 and 4a.

The contact clamps 5 consist of a flexible inflatable envelope 6, within a rigid metal ring 7 which may cause the metal clamping members 5 to grip the casing 3 when the flexible envelope 6 is subjected to internal fluid pressure which may be either gas or liquid.

The clamping members 5 are connected to conductor support members 9 as by the depending conductors 10, and the conductor supports 9 are connectedby flexible conductors 11 to the main power supply transformer and associated electrical equipment (not shown) that conventionally supply electrical power to the electrodes of an electric arc furnace.

In addition to being supported by the contact clamps 5, the cylindrical metal casing 3 is also supported by a pressure clamp, indicated generally at 12, which includes a flexible, inflatable member 13 within a rigid ring 14, and which may be made to tightly grip the casing 3 when the flexible member 13 is subjected to an internal pressure of fluid in the form of either gas or liquid in any conventional manner.

This type of electrode and casing support is conventional in self-baking electrode furnaces and the construction and operation are well known and understood by those versed in the art. The pressure clamp assembly 12 is attached to a support header 15 by means of hydraulic cylinders 16 and cooperating piston rods 17. As in common practice, when the pressure clamp assembly 12 is moved downward by the hydraulic cylinders 16 while, at the same time the pressure clamp is made to grip the cylindrical casing 3, the casing will be slidably moved downward through the contact clamps 5.

And conversely, when the pressure clamp assembly 12 is released until it no longer grips the casing 3, it may be moved upward relative to the casing, thereby preparing for further downward movement of the casing, if and when necessary.

The support header 15 is attached to a structure including the rods 18, connected at their lower ends to the conductor support members 9, as indicated at 19, and at their upper ends to the hydraulic cylinders 20, as indicated at 21. The piston rods 22 of the cylinders are connected to a suitable support 23 as indicated at 23'. The hydraulic cylinders 20 and piston rods 22 thereof, may be actuated to move the entire electrode column up or down relative to the furnace as desired.

The horizontal support member 24 is carried by the upper portions of the rods 18., and forms a part of the structure suspended from the hydraulic cylinders 20. A nonrotating contact and bearing 25, having a partially spherical central socket 26, is mounted upon the horizontal support member 24.

A companion rotating, semispherical contact and journal 27 is rotatable within the socket 26 of the nonrotating contact and bearing 25. The rotating contact and journal 27 are rigidly attached to the exterior of the upper end portion of a metal tube 28.

The metal tube 28 is suspended from the rotating contact and journal 27 and extends downwardly therefrom concentric to the axis of the cylindrical casing 3, and terminates at a proper distance below the bottom of the contact clamps 5.

A suitable section of the tube 28, preferably the lower end portion thereof as shown in FIG. 1, is threaded on the exterior with a coarse, deep screw thread as indicated at 29. The wall of the tube 28 is formed of a double shell having a space 30 therebetween whereby it may be fluid cooled or heated by any conventional means, either liquid or gas.

The entire tube 28, including the threads 29 thereon, the rotating contact and journal 27, and the nonrotating contact and bearing 25 are all formed of a suitably strong and conductive metal. The bearing surface between the rotating contact and journal 27 and the nonrotating contact and bearing 25 is made in such manner as to carry heavy weight and, at the same time, conduct heavy electrical currents While rotating as well as while stationary.

Suitably sized flexible conductor cables 31 are connected at one end to the nonrotating contact and bear ing 25, the other ends thereof being adapted to be connected to various electrical apparatus as hereinafter described.

For the purpose of rotating the tube 28 when desired, a rotational power unit is provided. For the purpose of illustration only this is indicated as a motor 32 carried by the horizontal support member 24, a bevel pinion 33 upon the shaft of the motor and a bevel gear 34 fixed upon the exterior of the tube 38 and meshing with the pinion 33. Any conventional electric circuit may be provided for the motor 32 with conventional switch means therein for closing the circuit to the motor when desired.

The hereinbefore described rotating tube with screw threads thereon, with its rotating contact and journal and its stationary contact and bearing and support structures, together with means for rotating such tube as desired, and also with means for conducting electrical currents to and through said tube comprise a part of this invention which functions usefully with other parts hereinafter described.

One method whereby the benefits of this invention may be attained could be achieved by connecting the conducting system 29, 28, 27, 25 and 31 to the same main transformer or electrical power source conventionally connected to the flexible conductor 11, thereby causing a portion of the electrical power of the furnace to enter the electrode at its center, at the area of 29, and generating heat in the central portion of the electrode 4b.

Another arrangement of the invention is illustrated in FIG. 2, in which is seen a three-phase transformer with its low voltage windings 35 connected to the electrodes 4b by the flexible cables 31, the contacts 25 and 27, and the tube assembly 28 and 29. The high voltage windings 36 of the transformer are connected to capacitors 37 by conductors 38.

Circuit breakers 39 are located in the circuit for connecting the high voltage windings 36 to the capacitors 37, or disconnecting them therefrom, or for changing the amount of capacitance connected to the high voltage windings.

Although the purposes of the invention may be achieved by any one of several possible configurations of the windings of the transformer, a delta-delta arrangement is shown in FIG. 2 for simplicity. Conventional means is diagrammatically indicated at 40 for changing the number of turns of the high-voltage windings 36 whereby the ratio between the low-voltage and high-voltage windings o the transformer may be changed. I

The interior of the tube 28 is kept supplied with carbon paste, which may be in the form of chunks as indicated at 41 in FIG. 1. The carbon paste descends in the tube by gravity, or by reason of a gas pressure which may be maintained above it, to completely fill the cavity left as the electrode 4b is forced downward by the screw 29.

OPERATION In the operation of an electric furnace equipped with the self-baking electrodes embody-ing the invention, the cylindrical casing 3, supported by the pressure clamps 14 and contact clamps 5, is adjusted to the proper position in the furnace by the hydraulic cylinders 16 and 20. Electric power is furnished to the cylindrical casing 3 through the contact clamps 5, depending conductors 10, conductor supports 9 and flexible cables 11 leading to the main power supply transformer (not shown).

The support tube 28 may be connected through the rotating contact and journal 27, stationary contact and bearing 25 and flexible conductors 31 either with the main power supply transformer or with power factor correctional devices as diagrammatically shown in FIG. 2 and above described.

Carbon paste 4 is continually supplied to the interior of the cylinder 3 through the open upper end thereof and the same is heated by the electric current passed therethrough, becoming plastic and entirely filling the lower portion of the cylinder, as indicated at 4a, and then being baked or cured and becoming a hard carbon electrode, as indicated at 4b.

Whenever the lower portion of the hard carbon electrode 4b is sufiiciently burned away, the motor 32 may be operated to rotate the tube 28 in proper direction so that the screw threads 29 thereon will force the electrode further down through the casing 3 into the furnace charge 1.

Workmen are also continually supplying carbon paste to the interior of the tube 28 as indicated at 41, and the same becomes plastic, as indicated at 41a, entirely filling the opening formed in the center of the hard carbon electrode 4b by the screw threaded lower end 29 of the tube 28.

It will thus be seen that neither the metal cylindrical casing 3 nor the metal supporting tube 28 is fed into the furnace charge, only the hard carbon electrode 4b being slidably moved downward out of the lower end of the cylindrical casing 3 by rotation of the threaded lower end 29 of the tube 28.

From the above it will be evident that the essential feature of the invention is the centrally located tubular support 28 terminating at its lower end in the coarse screw 29 embedded in the hardened portion 4b of the electrode, with means 32, 33, 34 for slowly turning the screw 29 so as to force the elctrode down as through the casing 3 as needed.

It will also be seen that until and unless the pressure clamp assembly 12 is released, the hard carbon electrode 411 is extruded from the bottom of the casing 3 by proper rotation of the screw 29. It will also be evident that only if the feed screw 29 is rotated with the pressure clamp assembly 12 released, will the casing 3 be carried downward through the contact clamp 5 along with the electrode. This insures that the use of the casing 3 in the furnace charge may be limited to that amount inadvertently burned away at the point where the lower end thereof emerges from the bottom of the contact clamps 5.

It will also be seen that, by reason of the transformercapacitor combination of FIG. 2 connected to the tubular column 28, very heavy electrical currents may be made to flow in the tubular column 28, the screw 29 and the central portions of the electrode 4b immediately around and below the feed screw. The heating effect of these currents, together with the heat-conducting effect of the screw, is most beneficial to the proper curing of the electrode.

Furthermore, it should be understod that the tubular support column 28 and screw 29 may be fluid cooled or heated by any suitable liquid or gas to any necessary degree. The outer surface of the screw 29 should be kept at temperatures consistent with coking of the electrode, while the interior surface of the screw and tubular column should be kept at temperatures consistent with a plastic state of carbon paste.

It will further be obvious that by keeping the interior of the tube 28 supplied with carbon paste which descends by gravity, or by reason of a gas pressure maintained above, it will completely fill the cavity left as the electrode is forced downward by rotation of the screw, thus forming a solid, homogeneous carbon electrode which is inserted into the furnace charge without either an outside metal casing or interior metal reinforcing.

It will also be seen that a desirable feature of the invention is that the electrical currents associated with reactive-kilovolt-ampere component of the power may be kept from flowing through the main power supply transformer and the associated electrical equipment that conventionally supply electric power to the electrode by way of the flexible conductors indicated at 11. Instead, the current associated with the reactive-kilovolt-ampere component of the power may be made to flow to power factor correctional devices independently connected to the electrode as shown in FIG. 2 and heretofore described.

It should be pointed out that although the principle of connecting power factor correctional equipment to the low-voltage structure of an electric furnace functions to assist in curing and hardening a self-baking electrode, it should be understood that this unique method of correcting power factor on an electric furnace is not limited to electric furnaces with self-baking electrodes. Power factor correctional equipment connected as above described and illustrated in FIG. 2 improves the operation of any electric furnace in that it relieves the main supply transformers and associated electrical equipment of a considerable part of the load, namely, that portion of the current associated with reactive power which is offset by action of circuit capacitance, as above described.

It should also be understood that although the arrangement described an illustrated herein shows dielectric or static capacitors as the power factor correctional equipment, this is by way of simplicity of disclosure only and other suitable power factor correctional devices such as rotary condensers or the like are equally useful for this purpose.

The benefits of the present invention may be realized without recourse to electrical apparatus of any description being connected to the centrally located tube 28 or feed screw 29. In such case, the metal mass of the feed screw is so proportioned and its conductive-magnetic properties so arranged that it will be heated by internally circulating currents arising from and induced by electromagnetic induction from electrical currents flowing into the electrode by way of the contact clamps 4. Such induction-heating effect may be clearly enhanced by constructing the feed screw of metal having magnetic properties.

We claim:

1. A self-baking electrode for electric arc furnaces comprising a vertically disposed metal casing, means for suspending the casing with its lower portion in a furnace and its lower end spaced above the furnace charge, a metal tube suspended concentrically through said casing, external screw threads on said tube, the upper end of the casing being open so that carbon paste may be placed therein, means for connecting the casing to a source of electrical power so that the carbon paste in the casing will first become plastic and then be baked into a hard carbon electrode, and means for rotating the tube so that the screw threads thereon will force the hard carbon electrode downward out of the tube and into the furnace charge.

2. A self-baking electrode as defined in claim 1 in which the upper end of the tube is open so that carbon paste may be placed therein, and in which the carbon paste in the tube becomes plastic and fills the cavity left in the center of the hard carbon electrode as it is forced downward by the screw.

3. A self-baking electrode as defined in claim 1 in which the lower screw threaded end of the tube extends downward below of the lower end of the casing and the upper end of the tube extends upward above the upper end of the casing.

4. A self-baking electrode as defined in claim 1 in which there is means for connecting the tube to a source of electric power.

5. A self-baking electrode as defined in claim 4 in which the casing and the tube are both connected to the same source of electric power.

6. A self-baking electrode as defined in claim 1 in which there is means for connecting the tube to power factor correctional equipment.

7. A self-baking electrode as defined in claim 1 in which a tube is connected to the low voltage windings of a transformer and the high voltage windings of the transformer are connected to power factor correctional equipment.

8. A self-baking electrode as define in claim 7 in which the power factor correctional equipment comprises capacitors.

9. A self-baking electrode as defined in claim 7 in which circuit breakers are located between the high voltage windings and the power factor correctional equipment.

10. A self-baking electrode as defined in claim 4 in which there is a rotating contact and journal fixed upon the exterior of the tube rotatably supported in a nonrotating contact and bearing.

11. A self-baking electrode as defined in claim 1 in which the means for connecting the casing to a source of electric power includes contact clamp means upon the exterior of the casing, a supporting structure from which the contact clamp means is suspended, pressure clamp means on the exterior of the casing and adjustably supported from said supporting structure, and means for adjustably supporting said supporting structure.

12. A self-baking electrode as defined in claim 11 including a horizontal support member in said supporting structure, a nonrotating contact and bearing mounted upon said horizontal support member, and a rotating contact and journal fixed upon the exterior of the tube and rotatably mounted in said monrotating contact and bearmg.

13. A self-baking electrode as defined in claim 12 in which the means for rotating the tube includes a motor and gearing operatively connecting the motor and the tube.

14. A self-baking electrode as defined in claim 1 in which the walls of the tube comprise spaced shells having a space therebetween whereby the tube may be fluid temperature regulated.

References Cited UNITED STATES PATENTS 1,596,902 8/1926 Taylor 1314 X 2,458,272 1/ 1949 Jones 13-14 2,778,865 1/ 1957 Kongsgaarden 13--16 2,899,667 8/ 1959 Bredtschneider 139 X 3,268,633 8/1966 Jansen 264-27 3,286,003 11/1966 Bullough et a1. 26429 3,365,533 1/ 1968 Alexander 139 X HIRAM B. GILSON, Primary Examiner US. Cl. X.R. 13-18 

